Lower Cosumnes River Watershed Assessment December 2006 Photos by The Nature Conservancy and Robertson-Bryan, Inc., Lower Cosumnes River Watershed Assessment 13501 Franklin Boulevard Galt, CA 95632 Prepared by: 9888 Kent Street Elk Grove, CA 95624 (916) 714-1801 December 2006 Lower Cosumnes River Watershed Assessment Table of Contents 1 INTRODUCTION ............................................................................................................. 1 1.1 Purpose and Intended Use of the Document....................................................................... 1 1.2 Document Organization................................................................................................ 2 2 GEOGRAPHIC SCOPE...................................................................................................... 3 2.1 General Watershed Characteristics................................................................................... 3 2.2 Cosumnes River Preserve Management Area ....................................................................... 7 3 WATERSHED CHARACTERIZATION...................................................................................... 9 3.1 Hydrology ............................................................................................................... 9 3.1.1 Precipitation ................................................................................................... 9 3.1.2 Historical Flow Patterns.................................................................................... 12 3.1.3 Historical Peak flows and Floods......................................................................... 14 3.2 Floodplain Topography and Geomorphology.................................................................... 16 3.2.1 Dillard Road to Wilton Road ............................................................................. 17 3.2.2 Wilton Road to Highway 99............................................................................ 19 3.3 Water Resources ...................................................................................................... 24 3.3.1 Surface Water Resources................................................................................... 26 3.3.2 Groundwater Resources ................................................................................... 27 3.3.3 Flood Protection Facilities ................................................................................. 29 3.3.4 Water Quality .............................................................................................. 31 4 COSUMNES RIVER PRESERVE RESOURCE CHARACTERIZATION .................................................. 33 4.1 Land Use .............................................................................................................. 36 4.1.1 Sacramento County General Plan........................................................................ 37 4.1.2 Elk Grove General Plan.................................................................................... 37 4.1.3 Galt General Plan .......................................................................................... 40 4.1.4 The Town of Thornton .................................................................................... 40 4.2 Biological Resources................................................................................................... 40 4.2.1 Vegetation................................................................................................... 40 4.2.2 Wildlife....................................................................................................... 53 4.2.3 Aquatic Resources.......................................................................................... 74 4.3 Cultural Resources .................................................................................................... 85 4.3.1 Introduction.................................................................................................. 85 4.3.2 Records Search Methods.................................................................................. 85 4.3.3 Records Search Results ..................................................................................... 85 4.3.4 Overview of Cultural Resources.......................................................................... 86 Cosumnes River Management Plan Robertson-Bryan, Inc. The Nature Conservancy page i Lower Cosumnes River Watershed Assessment 4.4 Key Restoration Projects and Research Studies ................................................................... 87 4.4.1 Riparian Forest Restoration by Planting .................................................................. 87 4.4.2 Floodplain/Riparian Restoration by Levee Breaching................................................... 87 4.4.3 Managed Wetlands........................................................................................ 87 4.4.4 Research at the Cosumnes River Preserve................................................................ 88 4.4.5 Managing Surface Water-Groundwater to Restore Fall Flows in the Cosumnes River........... 88 4.4.6 Cosumnes River Flow Augmentation Project ........................................................... 89 5 REFERENCES ................................................................................................................ 91 List of Tables Table 3-1. Average Monthly Streamflow by Water Year Type for Water Years 1960 to 2004................ 13 Table 3-2. Peak flows at selected recurrence intervals and locations on the Cosumnes River......................... 14 Table 3-3. Hourly peak flow events equal to or exceeding the 5-year recurrence interval (22,500 cfs). ....... 15 Table 4-1. Summary of Cosumnes River Preserve Land Holdings. ....................................................... 33 Table 4-2. Land Use Zone Definitions ...................................................................................... 36 Table 4-3. Vegetation Crosswalk Table. ................................................................................... 41 Table 4-4. Special–Status Plant Species Known to Occur in the Study Area. ....................................... 48 Table 4-5. Farming and Wildlife Activities.................................................................................. 60 Table 4-6. Special-Status Fish. ............................................................................................... 77 List of Figures Figure 2-1. Cosumnes River, Dry Creek, and Mokelumne River watersheds.............................................. 4 Figure 2-2. Cosumnes River watershed showing the major geologic regions, fault zones, and stream raches.......... 5 Figure 3-1. Mean annual precipitation for the Cosumnes and Mokelumne river watersheds. ........................ 10 Figure 3-2. Typical average monthly precipitation at various locations in the Cosumnes and Mokelumne watersheds. ........................................................................................ 11 Figure 3-3. Average Daily Streamflow for Water Years 1960 to 2004. ............................................. 13 Figure 3-4. Average Monthly Streamflow for Water Years 1960 to 2004.......................................... 13 Figure 3-5. Profile of the Cosumnes River and Deer Creek floodplain at RM 25.4. ................................. 18 Figure 3-6. Profile of Cosumnes River and Deer Creek floodplain at RM 23, upstream of the Folsom South Canal. ............................................................................................ 20 Figure 3-7. Aerial view of the Cosumnes River, floodplain, and Folsom South Canal looking west. ............... 20 Robertson-Bryan, Inc. Cosumnes River Management Plan page ii The Nature Conservancy Lower Cosumnes River Watershed Assessment Figure 3-8. Profile of the Cosumnes River floodplain at RM 12, showing the Cosumnes River Overflow Channel................................................................................................ 21 Figure 3-9. Cosumnes River looking north above Highway 99 showing the confluence with Deer Creek. ........ 22 Figure 3-10. Cosumnes River at a flow of approximately 10,000 cfs on March 25, 2005. ....................... 23 Figure 3-11. Profile of the Cosumnes River floodplain at RM 8.1, including Badger Creek........................... 23 Figure 3-12. Water Districts in the study area. ............................................................................... 25 Figure 3-13. Groundwater contour map of the IRMP study area. ........................................................ 28 Figure 3-14. Groundwater subbasins delineated in the Water Forum Agreement. ...................................... 30 Figure 4-1. Cosumnes River Preserve Land Holdings....................................................................... 35 Figure 4-2. Land Use Zones Surrounding the Lower Cosumnes River Watershed..................................... 38 Figure 4-3. Vegetation Types in the Preserve............................................................................... 39 List of Appendices A Cosumnes-Mokelumne Rivers Floodplain Reports and Studies B Cosumnes River Preserve Study Area Topographic Maps C Cosumnes Watershed Levees D Plant List for the Cosumnes River Preserve E Invasive Non-native Plant Species Managed at the Cosumnes River Preserve F Bird Species Known to Occur in the Cosumnes River Preserve Study Area G Animal Species Known to Occur in the Cosumnes River Preserve Study Area H Special-status